Hafrahvammagljufur Is (the most spectacular canyon in Iceland.
about 15 kilometres long and almost 200 metres deep. In many
places near Ytri-Karahnjukur, It is just under 100 metres wide.
The canyon was created when Jökulsa a Dal cut its way through
the moberg (tuff) ridge Karahnjukar and many other types of rock
from successive eras of geological history, which can be clearly
seen in the exposed cliffs. Hafrahvammagljufur submerged since
the Karahnjukar dam is built.

The canyon was named long ago after the so-called Hafrahvammar,
but in recent years, the southem area has acquired the name
Dimmugljüfur (Dark canyon). Hafrahvammar consists of grassy
hollows on the west side of the canyon area near Ytri
Karahnjukur. Nearly 500 metres above sea level there are many
interesting moberg (tuff) cliffs and shelves here, and a great
variety of Vegetation. There is a large cave in the Innermost
section of the hollows called Magnahellir. Shepherds used to
take shelter there, and it is named after one of them, Magni
from the farm Bru. A folk tale recorded by Sigfus Sigfusson
relates that Magni once left a piece of meat there, from his own
provisions, for the troll wife's children. Opening into the
canyon is the ravine Skessugja, or the troll wife’s gap. It is
about 150 metres long, and it can be reached from the north side
by a reasonably easy trail. a